224 research outputs found
Proximity Effect in Normal Metal - High Tc Superconductor Contacts
We study the proximity effect in good contacts between normal metals and high
Tc (d-wave) superconductors. We present theoretical results for the spatially
dependent order parameter and local density of states, including effects of
impurity scattering in the two sides, s-wave pairing interaction in the normal
metal side (attractive or repulsive), as well as subdominant s-wave paring in
the superconductor side. For the [100] orientation, a real combination d+s of
the order parameters is always found. The spectral signatures of the proximity
effect in the normal metal includes a suppression of the low-energy density of
states and a finite energy peak structure. These features are mainly due to the
impurity self-energies, which dominate over the effects of induced pair
potentials. For the [110] orientation, for moderate transparencies, induction
of a d+is order parameter on the superconductor side, leads to a proximity
induced is order parameter also in the normal metal. The spectral signatures of
this type of proximity effect are potentially useful for probing time-reversal
symmetry breaking at a [110] interface.Comment: 10 pages, 10 figure
Planar Laser Induced Fluorescence Mapping of a Carbon Laser Produced Plasma
We present measurements of ion velocity distribution profiles obtained by
laser induced fluorescence (LIF) on an explosive laser produced plasma (LPP).
The spatio-temporal evolution of the resulting carbon ion velocity distribution
was mapped by scanning through the Doppler-shifted absorption wavelengths using
a tunable, diode-pumped laser. The acquisition of this data was facilitated by
the high repetition rate capability of the ablation laser (1 Hz) which allowed
the accumulation of thousand of laser shots in short experimental times. By
varying the intensity of the LIF beam, we were able to explore the effects of
fluorescence power against laser irradiance in the context of evaluating the
saturation versus the non-saturation regime. The small beam size of the LIF
beam led to high spatial resolution of the measurement compared to other ion
velocity distribution measurement techniques, while the fast-gated operation
mode of the camera detector enabled the measurement of the relevant electron
transitions
Entanglement of a qubit with a single oscillator mode
We solve a model of a qubit strongly coupled to a massive environmental
oscillator mode where the qubit backaction is treated exactly. Using a
Ginzburg-Landau formalism, we derive an effective action for this well known
localization transition. An entangled state emerges as an instanton in the
collective qubit-environment degree of freedom and the resulting model is shown
to be formally equivalent to a Fluctuating Gap Model (FGM) of a disordered
Peierls chain. Below the transition, spectral weight is transferred to an
exponentially small energy scale leaving the qubit coherent but damped. Unlike
the spin-boson model, coherent and effectively localized behaviors may coexist.Comment: 4 pages, 1 figure; added calculation of entanglement entrop
Full counting statistics of a chaotic cavity with asymmetric leads
We study the statistics of charge transport in a chaotic cavity attached to
external reservoirs by two openings of different size which transmit non-equal
number of quantum channels. An exact formula for the cumulant generating
function has been derived by means of the Keldysh-Green function technique
within the circuit theory of mesoscopic transport. The derived formula
determines the full counting statistics of charge transport, i.e., the
probability distribution and all-order cumulants of current noise. It is found
that, for asymmetric cavities, in contrast to other mesoscopic systems, the
third-order cumulant changes the sign at high biases. This effect is attributed
to the skewness of the distribution of transmission eigenvalues with respect to
forward/backward scattering. For a symmetric cavity we find that the third
cumulant approaches a voltage-independent constant proportional to the
temperature and the number of quantum channels in the leads.Comment: new section on probability distribution and new references adde
The excitation spectrum of mesoscopic proximity structures
We investigate one aspect of the proximity effect, viz., the local density of
states of a superconductor-normal metal sandwich. In contrast to earlier work,
we allow for the presence of an arbitrary concentration of impurities in the
structure. The superconductor induces a gap in the normal metal spectrum that
is proportional to the inverse of the elastic mean free path l_N for rather
clean systems. For a mean free path much shorter than the thickness of the
normal metal, we find a gap size proportional to l_N that approaches the
behavior predicted by the Usadel equation (diffusive limit). We also discuss
the influence of interface and surface roughness, the consequences of a
non-ideal transmittivity of the interface, and the dependence of our results on
the choice of the model of impurity scattering.Comment: 7 pages, 8 figures (included), submitted to PR
Full Counting Statistics of Multiple Andreev Reflections in incoherent diffusive superconducting junctions
We present a theory for the full distribution of current fluctuations in
incoherent diffusive superconducting junctions, subjected to a voltage bias.
This theory of full counting statistics of incoherent multiple Andreev
reflections is valid for arbitrary applied voltage. We present a detailed
discussion of the properties of the first four cumulants as well as the low and
high voltage regimes of the full counting statistics. The work is an extension
of the results of Pilgram and the author, Phys. Rev. Lett. 94, 086806 (2005).Comment: Included in special issue Spin Physics of Superconducting
heterostructures of Applied Physics A: Materials Science & Processin
Aspects of metallic low-temperature transport in Mott-insulator/ band-insulator superlattices: optical conductivity and thermoelectricity
We investigate the low-temperature electrical and thermal transport
properties in atomically precise metallic heterostructures involving
strongly-correlated electron systems. The model of the Mott-insulator/
band-insulator superlattice was discussed in the framework of the slave-boson
mean-field approximation and transport quantities were derived by use of the
Boltzmann transport equation in the relaxation-time approximation. The results
for the optical conductivity are in good agreement with recently published
experimental data on (LaTiO/(SrTiO superlattices and allow us to
estimate the values of key parameters of the model. Furthermore, predictions
for the thermoelectric response were made and the dependence of the Seebeck
coefficient on model parameters was studied in detail. The width of the
Mott-insulating material was identified as the most relevant parameter, in
particular, this parameter provides a way to optimize the thermoelectric power
factor at low temperatures
Quantum-Limited Measurement and Information in Mesoscopic Detectors
We formulate general conditions necessary for a linear-response detector to
reach the quantum limit of measurement efficiency, where the
measurement-induced dephasing rate takes on its minimum possible value. These
conditions are applicable to both non-interacting and interacting systems. We
assess the status of these requirements in an arbitrary non-interacting
scattering based detector, identifying the symmetries of the scattering matrix
needed to reach the quantum limit. We show that these conditions are necessary
to prevent the existence of information in the detector which is not extracted
in the measurement process.Comment: 13 pages, 1 figur
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